1. Field of the Invention
This invention relates to an apparatus for generating, recording or reproducing sound source data. More particularly, it relates to such apparatus according to which adaptive data compression or looping taking advantage of the periodicity of the musical input sound signal may be realized efficiently.
2. Description of the Prior Art
In general, a sound source used in an electronic musical instrument or a TV game unit may be roughly classified into an analog sound source composed of, for example, VCO, VCA, and VCF, and a digital sound source such as a programmable sound generator (PSG) or a waveform ROM read-out type sound source. As a kind of the digital sound source, there has come to be known a sampler sound source which generates sound source data by sampling and digitizing live sounds of musical instruments and stores the resulting data in a memory.
Since a large capacity memory is generally required with the sampler sound source for storing sound source data, various techniques have been proposed for memory saving. Typical of these are a looping taking advantage of the periodicity of the waveform of the musical sound and bit compression by non-linear quantization.
The above mentioned looping is also a technique for producing a sound for a longer time than the original duration of the sampled musical sound. Considering the waveform of, for example, a musical sound, in the waveform portions other than the formant portion directly after start of sound generation, exhibiting inexplicity waveform periodicity, the same waveform appears repeatedly at a fundamental period corresponding to the pitch or height of the musical sound. Hence, by grouping an n number of periods of the repetitive waveform, n being an integer, as a looping domain, and repeatedly reproducing the looping domain, if so required, sustained sounds may be produced for a prolonged time with only a small memory capacity.
On the other hand, for bit compression of ordinary audio PCM signals, a system employing a feed forward type filter on the encoder side is generally employed. This system transmits sub-data, that is the data concerning compression, in addition to the compressed data, with the filter on the decoder being an IIR (Infinite Impulse Response) or recursive digital filter. Such system is already adopted in, for example, digital optical disk standards.
Meanwhile, sampling the musical sound and looping its tone component is tantamount to connecting and repeatedly looping the looping start and end points of the looping domain. In this case, it is necessary for these looping start and end points to be approximately equal to each other. The reason is that, if otherwise, that is, if discontinuities are present at the connecting points, looping noise is likely to be produced.
However, it is difficult to select the looping start and end points to be substantially equal to each other, by reason of the sampling periods, so that an efficient solution has not be provided by the hitherto known looping method.
Some sounds are devoid of the looping domain, such as those from percussion.
It is noted that, when reading out the sound source data from the memory in which the sound source data are stored, data start address data and looping start address data of the sound source are indicated in a directory which is on the same space as the memory space having the sound source data. These two address data usually have different values. When these address data are permanently loaded in, for example, an address register of an audio signal processing apparatus, an increased number of times of memory fetching represents an increased load especially in case of time division signal processing for generating plural sounds.
On the other hand, the looping domain may or may not be present in the sound source data of the sampler sound source which is to be read out from the memory for reproduction. The processing method for terminating the reproduction of the sound source data depends on whether there is or there is not the looping domain in the sound source data. When terminating the reproduction of the sound source data having the looping domain, it is customary to utilize a looping end point flag included in the sound source data of the looping domain. When terminating the reproduction of the sound source data devoid of the looping domain, suitable measures must be taken to terminate the sound at a predetermined position of the sound source data. Usually a separate address is provided for the reproduction terminating signal.
Thus, when the processing method for terminating the reproduction of the sound source data differs depending on the presence or absence of the looping domain, it is necessary to provide the sound source device performing the above processing operations with separate addresses for the reproduction terminating signals for sound source data devoid of the looping domain and data indicating the presence or absence of the looping domain, thus resulting in an increased memory capacity and a complicated structure of the device.